T-Mobile US Inc. plans to sell $2 billion in debt after raising nearly that amount in a stock sale, as the company beefs up its war chest for acquiring wireless spectrum.

The fourth-largest U.S. wireless carrier said in a filing Monday it could use the money for a number of purposes including spectrum purchases, a goal it has been open about recently. The company also said Monday it had raised a net $1.8 billion from a sale of stock...